This Project is one in which a number of laboratories outside the Center, both local and elsewhere, will obtain YACs from a wide variety of genomic regions of special interest. Thus, it is directly involved in the sharing of resources, in outreach to other laboratories and Centers, and in the testing of alternative technologies both for the assembly of YAC contigs and for the verification and further analysis of YACS. This project is based directly on the function of the screening Laboratory, using primer pairs obtained from investigators outside the P50 Center to locate cognate YACs by screening with the polymerase chain reaction. The screening method will be that outlined in the Choice Approach section of the Center proposal. Over the first three years, the goal is to screen for up to 1500 primer pairs, including as many as 600 for particular genes of interest; 300 that collectively cover 1 to 4 Mb regions; and 600 for chromosome 4. In several cases, particularly HLA, the analysis will be pursued here at Washington University -- for example, to determine if YACs from the two copies of chromosomes 6 can be organized separately; and in some cases, the regions being studied will be from chromosomes 7 and X, and will thereby contribute directly to Projects 2 and 3.